Power tools, such as screw drivers, nut runners, drills, are typically equipped with at least one detector arrangement of some form for sensing one or more parameter, such as for example relative angular displacement between two relatively moveable parts of the power tool. The one or more parameter may for example be used for monitoring purposes or feedback control.
The detector arrangements are depending on the application typically configured to measure either linear displacement or rotational displacement i.e. angular displacement.
The detector arrangements are also typically characterized as contact or non-contact detector arrangement depending if a physical contact with associated wiring to the relatively moveable measurement object is required or not by the detector arrangement.
Different detector arrangements are used today throughout a variety of different systems for sensing relative position i.e. displacement between two relatively moveable elements, such as between a rotatable element and a static element. These detector arrangements are typically referred to as synchros, resolvers, encoders, slip rings or transducers and operates based on physical sensing principles such as optical-, magnetic-, inductive-, capacitive- or eddy current physical sensing principles.
Optical detector arrangements typically implements a disc mounted on a rotatable measurement object such as a rotating shaft, wherein said disc is made of glass or plastic with transparent and opaque areas. These areas are exposed to light from a light source. The resulting light i.e. optical pattern is then received by a photo detector array which reads the optical pattern. The read optical pattern is then processed in order to obtain the position of the disc i.e. so as to provide the angle of the shaft.
Magnetic detector arrangements typically implements a series of equidistant magnetic poles provided in an alternating North-South pole configuration. The series of magnetic poles are mounted on a rotatable measurement object, such as a rotating shaft. A magnetic sensor (typically magneto-resistive or Hall Effect) then reads the magnetic pole positions. These positions can then be processed by a processing device so as to determine the angle of the shaft, in a similar to the above described optical detector arrangements.
Inductive detector arrangements typically implements inductive elements in the form of at least one first coil mounted on a rotatable measurement object, such as a rotating shaft, wherein said at least one first coil during rotation of the measurement object moves relative at least one second coil. By energising the at least one second coil, using alternating current (AC), a current is induced in the first coil due to mutual inductance. The degree of electrical connection between the at least one first coil and the at least one second coil being representative of the relative displacement between the at least one first coil and the at least one second coil.
Capacitive detector arrangements typically use a disc on a rotatable measurement object. Upon rotation of the measurement object the disc will change the capacitance between two electrodes of the capacitive detector arrangement, wherein said capacitance can be measured and processed to as to provide an indication of the angular displacement.
Eddy current detector arrangements typically uses a scale coded with high and low permeability, non-magnetic materials, which is detected and decoded by monitoring changes in inductance of an AC circuit that includes an inductive coil sensor.
However, the detector arrangements according to prior art tends to suffer from one or more of the following drawbacks: require large space, require complex circuit(s), cause high power consumption, are difficult to maintain, are costly to build, are sensitive to external magnetic fields, provides low accuracy and are prone to wear.
These drawbacks render unsuitable for use within a power tool since all these drawbacks adversely affects performance aspects and/or build costs for a power tool.
Accordingly, there is a need to present improvements in the art of detector arrangements for sensing relative displacement between relatively moveable parts of a power tool.